An important application of the current results will be in benchmark calculations of transverse momentum dependent cross sections, and in particular for the small transverse momentum region where the transition from collinear factorization to TMD factorization is expected to set in.
One motivation for the present project was to assess the possible role of limitations in collinear PDF and FF fits in explaining discrepancies between theory and data in the range of intermediate and large transverse momentum across a number of transversely differential processes [1]}, [2]}, [3]}, [4]}.
For this, a truly simultaneous analysis of parton distribution and fragmentation functions across the standard set of electromagnetic processes, integrated over all transverse momentum, is necessary.
The general success of the collinear fits for transverse momentum integrated cross sections that we have examined here, and their evident predictive power, suggests that factors unique to the transverse momentum differential treatment are responsible for the tension with data.
We plan to address this also in future work.
